1. Field of the Invention
The present invention concerns a device for switching the flow direction of a fluid which is connected to equipment using the fluid and having a fluid circulating path disposed at the inside thereof and used for switching the flow direction in the circulating path between the forward direction and the backward direction.
2. Description of the Prior Art
Existent rotary directional control valves have a structure, for example, as shown in FIGS. 8(a)-8(c) in which a directional control valve 81 has a partition plate 83 rotatably disposed in a cylinder 82 of a cylindrical shape. A first flow space X and a second flow space Y are formed on both sides of the partition plate 83. An inlet A on the primary side, a first exit/inlet C on the secondary side, an exit B on the primary side, and a second exit/inlet D on the secondary side are opened to the circumferential side of the cylinder 82 each at an angle of 90.degree. from each other. The inlet A on the primary side is connected to a fluid supply source, such as a pump P, and the exit B is connected to a flow destination of a fluid, such as a reservoir tank R. On the other hand, both of the exits/inlets C and D on the secondary side are connected to both ends of a circulating path of an equipment 9 using the fluid.
Then, when the control valve 81 is in a state shown in FIG. 8(a), since the first flow space X communicates the inlet A with the second exit/inlet D, and the second flow space Y communicates the exit B with the first exit/inlet C, the fluid flows to the equipment 9 on the secondary side in the direction indicated by the arrows shown in FIG. 8(a) (hereinafter referred to as a forward direction). then, when the control valve 81 turns to a state shown in FIG. 8(b), since the partition plate 83 closes the first and the second exits/inlets C and D, the fluid does not flow on the secondary side. Further, when the control valve 81 is in a state shown in FIG. 8(c), since the first flow space X communicates the inlet A with the first exit/inlet C, and the second flow space Y communicates the exit B with the second exit/inlet D, the fluid flows to the equipment 9 on the secondary side in the direction indicated by the arrows shown in FIG. 8(c) (hereinafter referred to as a backward direction).
Thus, the directional control valve 81 has a structure which is capable of switching the fluid flow direction on the secondary side between the forward and the backward directions by rotating the partition plate 83, without changing the fluid flowing direction on the primary side.
In the existent directional control valve 81 as described above, however, when the flow of the fluid on the secondary side is stopped with the ends of the partition plate 83 being placed on the first exit/inlet C and the second exit/inlet D or on the inlet A and the exit B, the partition plate 83 closes the flow ports so that no more fluid flows in the flow channel. Accordingly, in this stationary state, a load is wastefully exerted on the pump P that delivers the fluid in one direction and results in a concern that the pump may fail if such a state is left as it is for a long period of time.
Particularly, in a state where the partition plate 83 closes the first exit/inlet C and the second exit/inlet D, as shown in FIG. 8(b), the fluid pressure in the first flow space X in communication with the inlet A is increased which exerts a large load on the partition plate 83. This brings about a problem of deterioration of the endurance of the device, for example, by creating slack in the attaching portion of a rotational shaft.